h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Well, I intended to talk about plasma in general, but since that didn't seem to work, let's take on a different approach.

(As you probably already know,) rockets can achieve the same thrust by either ejecting more material at low velocities or less material at high velocities. The latter is perfered, since the material must be carried on board. It is my understanding that high velocities can be achieved by using plasma. From what I've read, the higher the temperature, the greater the velocity...? And as laboratory plasma can be up anywhere between 11,000 degrees Celsius and 110,000 degrees Celsius, my educated guess would be that you're getting a decent amount of velocity from using that.

Also, plasma is supposed to react well to magnetic and electronic fields. If you could power your rocket by plasma, could you control the direction by placing the magnetic fields in certain postitions/moving them there?

If this is your Ion drive, please excuse me....but is it?

You are confusing two different things.

The low thrust for a long time is the approach taken with both ion drive and bussard ramjets.

The other thing is high energy plasma giving increased thrust. It does, but you waste some plasma, so to keep your thrust up, you have to put in some more plasma, and a lot more energy.

This causes two problems.

first, as it is very hot, you have to be carefull not to melt your venturi chamber where your plasma is being ejected.

Second, due to the high energy requirements, you can't keep it up for long. (also the rate of ejection of plasma means that you rapidly run out of reaction mass). also due to the thrust, your ship has to be designed to take higher loads, which means more reinforcement, which means more weight, which means bigger engines, etc....

These two approaches are diametrically opposed.

Another low thrust technique is solar sailing, where you use the solar wind and/or light pressure to give you thrust. This only works for the inner solar system though.

Sorry to 'butt in' to this conversation, but there's a kind of rocket i thnik you'd both be very interested in, the VASIMR. This is a plasma engine with a unique characteristic: it can vary the velocity of the exhaust to match that of the spacecraft. The idea is that for a given power input, it starts off with high thrust and low velocity, and then moves to low thrust and high velocity as it gets faster, rather like changing gears on a car. VASIMR uses hydrogen as a propellant which it ionizes in an electrical discharge and then heats the hell out of in a magnetic bottle. The power would come from a nuclear reactor, but only indirectly: the reactor would be used to generate electrical power which would then heat the hydrogen.

Initial tests whow that VASIMR has a lot of promise. It is powerful and efficient, and could cut the time for a journey to Mars down to a matter of months: http://spaceflight.nasa.gov/mars/technology/propulsion/aspl/vasimr.html

There are a number of ways to improve earth-mars journeys, but considering the 10 MegaWatt power requirement for this engine, it currently isn't one of them.

The mars direct plan (which nasa are now using as the blueprint for it's manned mars mission program) deals with how to go there soon, using existing technology, and all it needs is a much smaller amount of money, and the will to go there.

Once you have a permanent base there, you can see about improving the efficiency of getting there, but if you don't use existing technology, you end up having the mars program being nothing more than a glorified moon shot.

The 10 Mw power requirement is *easily* fulfilled by putting a nuclear reactor into space, as their power to weight ratio is ideal for such a job. The technology exists, but too many people are squeamish about the word 'nuclear'. Hence the reason why hospitals have MRI scanners as opposed to NMR scanners.

Getting a human onto Mars using existing technology is no small feat. Space is about the most hostile environment one can imagine, and minimising the traveller's exposure to it is going to improve the chances of success no end.

yes, you put up a fission reactor, and then you have to surround it with a pressure vessel (not least of which for shielding). This all adds mass to your ship, and you get up to the 90 billion dollar bracket.

But you also are talking about orbital assembly on a level currently not even planned, yet alone attempted.

Alternatively, you can try the mars direct approach, now written up at A749928 which as you can see uses no new technology, and according to zubrin's book costs about 1/5th the cost of the original NASA plan which uses you approach.

not to mention, your approach leaves only a few days on the planet for exploration.

Nuclear reactors are hardly new technology, are they? You could use MHD technology to convert the heat to electrical energy without recourse to a pressure vessel. And the VASIMR rocket is hardly new either: it's been around in one form or another for 25 years.

Besides, cost shouldn't really be NASA's priority when sending people to Mars. If it were, why not dispense with humans and send robots (which do a much better job anyway )?

I also don't see how getting there a lot faster allows *less* time for exploration. Or perhaps I'm mssing something here.

nuclear reactors are not a new technology, they have been around for nearly 60 years, but there is a world of difference between something the size of 3-mile island or chernobyl, and something small enough to put into orbit.

The problems don't stop there though, as once you have got it in orbit, it has to be strong enough to take micro-meteorite impacts, the massive thrust you are developing, and has to be shielded sothat you don't nuke the astronauts.

as to robots being better, yes they are, but only for lunar exploration. once you get outside lunar orbit, you have to factor in things like the 16 minute round trip delay in commanding the robot, and the lack of intelligence of even the best automated systems. There is only so much that robots can do.

as for getting there faster resulting in less exploration time, this is caused by the celestial mechanics of the orbits of the two planets.

You can only transfer from one planet to the other when you have a launch window. outside this time, you are commiting suicide.

These launch windows are determined by the mission design inherent in the craft design parameters.

The original nasa idea effectively called for a dragster design, where you travel very fast to reduce the amount of time spent in zero gravity. To cause a significant reduction in time, you have to go very fast indeed, which means a lot of weight. it also means that you have to carry your fuel with you, and because of the fuel requirements, it means you have to use the fastest and most efficient orbits.

The problem with this is that the only return window back to earth is about 2 weeks after you arrive at mars (caused by the relative orbital positions and rates of the two planets). If you miss this window, you are stuck there for about 3 years, defeating the entire purpose of having a short journey time.

Mars direct, on the other hand is designed to make the NASA constarints irrelevant. It gets around the weight problem by not being bothered about fast orbits, and not carrying all the fuel for the return trip. it gets aroung the zero gravity time by using centrifugal gravity generation.

The return orbit has a massive launch window, with varying fuel requirements. If you need to abort the landing, it stays in orbit, and can have the fuel sent up to the station (which you build from spent fuel containers), or it can use the fuel it doesn't use to land to transfer into a low energy orbit which will take a while, but will get them back safely.

If you land, you can immediately refuel from the atmospheric fuel generators, and spend a lot of time exploring, by which time the fuel that you have used exploring will have been regenerated by the generators.

as for "cost shouldn't be an issue", of course it is. this determines how many missions you can send, and how often you can send them.

If you can send 5 missions for every 1 in the original plan, and you can spend six months exploring and working per mission, then within a few tens of years you have not only got a functional colony, but you have refueling depots covering large parts of the surrounding area.

you can then have those fuel generators send fuel up to your space station, and you can immediately start asteroid mining, setting yourself up for a self sufficient mars colony, and for exploration of the outer planets.

On the whole, I think I prefer mars direct ending with a colony, to a moon type program "to plant the footsteps of mankind on another world", followed by an immediate "been there, done that" which killed the 1970's space station and moon base plans.

Sorry I'm late, but...

I agree that cost is an issue, but to me it seems that your Mars Direct alternative is pretty darn expensive, too.

You were talking about these 'Atmospheric Fuel Generators'. Would these be attached to a vessel, or would they be the only thing going? If they were the only thing going, you would need to have them in some sort of rocket form to get to Mars. This requires quite some planning, and money, I'm sure. For instance, would the rocket (forgive me if there is a better term to use) be solely composed of the fuel generator(s), or would some parts 'break off' revealing the generator(s)?

Using existing technologies is a great idea. But whose going to pay for all this? You said it was not just theory, but have the Mars Society people actually built it? And it must have cost money to plan and build it out if they did, or it will if they haven't.

The only difference I see here is that Mars Direct uses more money to make sure everything works in theory and in use the first time, while other approaches use less money, but more often. Either way, you're both getting up there on your 90 billion bracket.

zubrin covers a lot of this ground in his book "the case for mars" (see my write-up at http://www.xyroth-enterprises.co.uk/b1996002.htm ) and I try and cover some of it off the review A749928 about mars direct.

Now to deal with some of the details you raise.

The fuel generators use a process that has been known about for many years, and which they managed to get working as a small scale production model for about $60,000 a while ago.

you mount them on a heavy lift rocket, which you must have anyway to travel to mars and send them on their way.

landing them on mars is no trickier than landing the viking probe.

they then start working, and the telemetry tells you when you have almost enough fuel for a return trip.

at this point you can send two more heavy lift rockets, one with a fuel generator, another with the habitation module.

the habitation module is sent with a set of abort options in its computers to maximise safety.

first, you can abort launch. then you can abort to orbit, then to a free-return orbit (as used by appolo 13) then to mars orbit, then to mars.

on mars you have access to the two functioning fuel generators, which you can use to power the habitation module if there are any problems.

After you have been there a while, you can return to mars orbit, using the same type of multiple abort program, using the fuel generated on mars.

Because of the redundancy in the plan, and the re-use of components, you end up with a set of usefull components as well.

heavy lift rockets letting you launch satelites many times their current weight, atmospheric fuel generators that can be used on both earth and mars, a commercial space industry, and a number of other benefits.

even the commity that estimated the one-shot monolithic atomic ship calculated that the cost would be 1/3rd the price.

and that is before you add in the benefits of the sustainable new technologies, and factor out the inefficiencies of government organisation.

it is thought that using the model used for building the X-33 spacecraft, you could take the cost down to $6,000,000,000 rather than the original $90,000,000,000.

and you get multiple extra levels of safety in the mars direct program.

add to that that even the most pessimistic valuers say that the lunar program paid for itself many times over, and it is both possible and feasible. all it needs is the will to do it.

It seems like a lot of buggering around just for the sake of avoiding having to upset some people through putting a nuclear reactor in space.

Yup. I must admit, I'm still too skeptical about the Mars Direct plan to like it better than having a nuclear reactor in space. But hey, if they can call NMR's MRI's, then we can change the name too, and send it up anyway.

But, if...or perhaps when...Mars Direct pleases the people it needs to and the mission starts, I'll like it more.

Maybe.

Having a colony at the end *is* more preferable than just having a few pictures.

small point about mars direct vs giant nuke.

the problem with the nuclear reactor plan isn't that it's nuclear, it's that it is blue skies technology and thus with a plan you can impliment today, it is unnecessary.

Also it is poor value for money. at 6 vs 90, you get 15 mars direct type missions for the price of one nuclear mission. That is colonisation levels of exploration, as opposed to being a "plant the flag" type mission.

What other criticisms of mars direct do you have?

pop over to the entry at A749928 , and post them there, and I will try and answer them as best I can.

It isn't blue skies technology: the VASIMR rocket has been around for 25 years in the lab. It's merely politcal considerations which have forestalled the use of reactors in space.

Basically, if I were an astronaut going to Mars I'd want to spend as little time on the journey as possible, for safety and health reasons. That's why I prefer the nuclear option.

True, the principle of vasimir has been know for 25 years. however in regards to a mars mission, there are a number of unsolved problems.

for a start, there is the 10MW power plant. These are currently BIG, and thus heavy. As you are talking about using it for a mars mission, you are talking about having a crew, so you need good shielding for your nuclear reactor, which is heavy, or you need the power plant to be on a long boom, which entails orbital construction at least as complex as for the space station.

Also, as the link you provided shows, you need the following technologies to be developed, most of which are not here yet.

Super conducting magnets at space temperatures.
Compact power generation and conditioning equipment.
Compact and robust radio frequency systems.
Hybrid magnetic nozzle.
Light weight heat shields and radiative cooling.

Most importantly though, the whole write up is predicated on the idea of wasting most of your energy to get there FAST. this is where the problem comes, because to go fast you need high exhaust velocities, which means strong space craft, which means orbital construction.

mars direct needs none of these things.

mars direct exchanges speed of travel for payload and price. you can decide to do mars direct today, and have the basis for a colonisation program within 10 years. with orbital construction, you are talking about a timeline of 30 years, and much more expensive technology.

this gives mars direct one advantage that all other plans that I have seen don't have. It is quick enough and cheap enough that it can be done in under a generation, and uses no fundamentally new technology that we have not already used to do it, so no sudden bad news surprises.

Even so, if new technologies come along you can easily fold them in to the mars direct plan. you can use them either to increase payload, or increase safety, or to reduce cost. but the new technologies are not required, only useful.

Ok.

If we could finish Mars Direct in under a generation, and it's cheap, we should start now. Is the mission going to start soon? What's the deal?

the deal is that NASA have accepted mars direct as the overall style of mission for manned exploration of mars, but they still have not quite got the main principle. Their version will (by mars direct standards) be massively overstaffed, resulting in much bigger ships, with the associated problems.

Also, they still need a politition with vision to decide that going is a good idea, and then fight for it in congress.

Currently it is most likely that either the mission will be long delayed (nasa talk about many years) or that it will be someone other than nasa that goes.

Lots of people are working to get something going that will actually happen.

Note: if the americans hadn't turned chicken over space spending after the moon program, we would already have a martian colony.

Hey, no backhanded comments!! We didn't 'turn chicken', we simply decided to spend that money on other things. Yeah...Besides, if you want a Mars colony, stop making fun of us, get together with your Boston Astronomy group, and do something. It's not like we're the *only* ones sitting here doing nothing. You are too.

I am not saying that the people turned chicken. every single survey says that the people want space, and the higher the level of education, the bigger the percentage that want it.

It is the politicians (as exemplified by senator proxmire) who turned chicken.

As to boston astronomers, I am trying to drum up business there, and I am also working on an article on mars direct for the pescu website (at http://www.pescu.net ) which will be among the first articles on the site.

So I am trying. so are my friends.

Goo, I'm gald someone is.

Now, to bring this discussion back on an even keel, I think we sheould abandon this notion of it being a forum for advocating one particular method of getting there over another. The whole point of what *I* am talking about is simply that more advanced technology = more options. There is probably no *right* way of exploring the planets, just priorities, constraints and objectives.